Samples microwave, acid-assisted

Sastre J, Sahuquillo A, Vidal M, Rauret G. Determination of Cd, Cu, Pb and Zn in environmental samples microwave-assisted total digestion versus aqua regia and nitric acid extraction. Anal. Chim. Acta 2002 462 59-72. 

Sediments and biota. Several sample digestion procedures (mostly between 0.1 and 1 g of freeze-dried sample) can be apphed such as (1) enzymatic digestion with lipase and protease (2) digestion with TMAH or KOH-EtOH or NaOH in methanol-water with or without microwave oven assistance (3) digestion with HCl and NaCl aqueous solution, with addition of ethyl acetate and methanol (4) extraction by supercritical CO2 (5) extraction by acetic acid. Often these digestions and extractions are accompanied by simultaneous extraction into an organic (or different organic) solvent such as hexane, dichloromethane, acetic acid-tropolone in hexane, and tropolone in dichloromethane, methanol or diethyl ether. 

The metal content analysis of the samples was effected by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES Varian Liberty II Instrument) after microwaves assisted mineralisation in hydrofluoric/hydrochloric acid mixture. Ultraviolet and visible diffuse reflectance spectroscopy (UV-Vis DRS) was carried out in the 200-900 nm range with a Lambda 40 Perkin Elmer spectrophotometer with a BaS04 reflection sphere. HF was used as a reference. Data processing was carried out with Microcal Origin 7.1 software. 

M.P. Colombini, R. Fuoco, A. Giacomelli, B. Muscatello, Characterization of Proteinaceous Binders in Wall Painting Samples by Microwave Assisted Acid Hydrolysis and GC MS Determination of Amino Acids, Studies in Conservation, 43, 33 41 (1998). 

Six samples (1-6) were digested using microwave-assisted acid procedures. Each sample was run in triplicate. 

Solvent-free conditions can also be applied without microwave assistance. In [24] reactions of o-PDA with several substituted chalcones were reported to have been carried out on neutral A1203 at 80°C with high yields (60-80%) of the target dihydrobenzodiazepines. Besides diazepines, some samples of benzothia-zepines 21 were also synthesized by the treatment of o/Y/70-aminothiophenol 19 with oc,(3-unsaturated ketones 20 on a silica gel surface (Scheme 4.6). The application of other solid supports like acidic, basic or neutral alumina,... 

Microwave-assisted digestion procedures are used for total metal analysis in aqueous samples (EPA Method 3015) and for solid or oily samples (EPA Method 3051). These procedures allow for a rapid sample digestion with nitric acid under high pressure and temperature conditions the addition of hydrochloric acid is optional. Samples... 

Methods involve extractions of analytes into organic solvents, as well as treatments with acidic or basic reagents. Solid-phase extraction can be used for removal and pre-concentrations of analytes in aqueous solutions. Applications of low-power focused microwave technology have been investigated as a means of dissolution, and good results have been reported for extractions of organometal-lic compounds of tin and mercury (Schmitt et al., 1996 Szpunar et al., 1996). Analyses of CRMs were used for verification. The time necessary for quantitative isolations of the analytes was greatly reduced, e.g. 24 h to 5 min. In addition, there were reductions in solvent volumes, and improvement in analyte recoveries. Some of the analytical procedures for speciation of particular elements such as mercury, described later in this chapter, include microwave-assisted sample preparation. 

Vaisainen, A. and R. Suontomo. 2002. Comparison of ultrasound-assisted extraction, microwave-assisted acid leaching and reflux for the determination of arsenic, cadmium and copper in contaminated soil samples by electrothermal atomic absorption spectrometry. J. Anal. At. Spectrom. 17 739-742. 

It should be noted that microwave-assisted extraction (MAE) discussed in this chapter is different from microwave-assisted acid digestion. The former uses organic solvents to extract organic compounds from solids, while the latter uses acids to dissolve the sample for elemental analysis with the organic contents being destroyed. Microwave-assisted digestion of metals is covered in Chapter 5. 

This laboratory experiment describes the preparation of a vegetation sample (e.g., grass) for radiochemical analysis. The sample is dried and ashed. In Part 12A, the ash is fused with sodium hydroxide and sodium carbonate to bring it into solution. An alternative method in Part 12B uses a microwave-assisted digestion technique with nitric and hydrofluoric acid. The prepared sample is suitable for radionuclide analysis, notably for radio-strontium or plutonium. 

---